I have been a BB user since the very beginning and had been enjoying 0.4 since it's release. I had been suffering from many of the same problems that others have been posting about - home screen redraws, slow response for certain apps, slow market etc. There seemed to be a general lagginess at times. I would swipe between homescreens for instance and it would take several tries before the phone responded. Not always, but enough to be annoying.
Another poster started a thread about one of the P3Droid kernels completely changing the responsiveness of his phone and I decided to give that a try. That ended up being an epic fail as not one of the P3Droid kernels would boot on my phone. I had been running Chevy01s MV 1.0Ghz kernel and as an experiment tried switching to Chevy01's LV 0.8Ghz kernel. The difference is unbelievable. Every problem that I had with the phone is now gone. Every screen pops up instantaneously when I select things. The homescreen redraws (using ADW launcher) are completely gone as well. The phone is much much snappier and runs cooler as well. This echos the result that the other poster had when he downgraded his clock speed as well.
For those of you having these or other issues, try one of the sub 1.0Ghz kernels. Use whatever you've been running (Chevy01, P3Droid, etc.) and go with the 0.8 version. If you're like me, you may be amazed at the difference. Maybe these phones just don't like going that fast.